DESCRIPTION: (Applicant's Description) Basic and applied research targeting large molecular objects and supramolecular self-assembly in general has been on a steady rise over the past decade. Molecular engineering has reached a point where virtually any complicated shape of a molecular object can be manufactured and certain desired properties achieved. A systematic approach to constructing such objects includes identifying efficient bonding mechanisms designed to hold the construction blocks together and yet not frustrating the assembly step. Now as chemists are capable of assembling more and more complicated systems, it became evident to us that the time has come for the next logical step in molecular manipulations, that is, to develop intelligent ways and rules of molecular disassembly. This requires the search for and development of molecular buckles and latches that can be selectively unfastened on demand. One foreseeable application of these fasteners, which is particularly relevant to the field of photobiology, is their utilization in the rational design of molecular hosts capable of photoreversible accommodation of organic guests. In our preliminary studies we have identified a robust system based on dithiane-carbonyl adducts that satisfies all the criteria of molecular assembly and yet is capable of site-specific disassembly when irradiated in the presence of electron-transfer sensitizers. During the course of the proposed research rational design will be applied to develop a series of novel molecular hosts comprised of crown ethers and/or cryptand units linked via our photolabile tethers. The complexation selectivity and photochemistry/photophysics of the novel molecular systems will be examined to evaluate the prospects of their application in photobiology, e.g. as potential carriers for photodynamic therapies etc.